1. Technical Field
The present invention relates to a method and apparatus for improving interexchange digital telephony in general and, in particular, to a method and apparatus for improving a telephone communications network having echo cancelers. Still more particularly, the present invention relates to a method and apparatus for measuring the performance of an echo canceler within a telephone communications network.
2. Description of the Related Art
A digital telephone communications network typically includes a transmitter and a receiver. The function of the transmitter is to put a series of signal pulses, usually shaped by some form of filters, onto the network. The function of the receiver is to detect the signal pulses as they are being sent from the far end of the network. Sometimes, the detection task is difficult because the signal pulses are being distorted during transmission. One source of distortion is caused by the coupling of the transmit signal pulses directly across a hybrid circuit and into the receiver input as "echoes." This is a common problem when operating on a two-wire system.
Generally, such transmit signal pulse echoes may be removed by an echo canceler. An adaptive filter is typically utilized to derive a function of the transmit signal for subsequent subtraction from the received signal. Although the transmission quality will be improved with the addition of an echo canceler, currently there is a lack of convenient techniques for monitoring the performance of these echo cancelers within the telephone communications network. Under the prior art, several pieces of test equipment are required to be connected externally from the telephone communications network in order to perform such echo-cancellation performance monitoring. Consequently, it would be desirable to provide an improved method and apparatus for measuring the performance of an echo canceler within a telephone communications network such that the need for external test equipment may be reduced or eliminated.